Wind and solar power are intermittent and generate power when available and not when needed, so large amounts of energy storage are required.
The technologies are diverse, from classic lithium-based “big battery” installations, through flow batteries, to molten salt batteries, iron-air batteries, gravity batteries or carbon dioxide expansion batteries.
Each technology has its advantages and disadvantages in terms of efficiency, size, location, installation costs, running costs, input and output powers, longevity and storage time of the device. ‘energy.
This is a good thing, because different solutions will cover different needs: some support the grid during instantaneous peaks in demand, others smooth out mismatched daily curves between renewable energy demand and supply, and others help solve seasonal supply dips, such as when solar power dims during the winter.
Today we are talking about another storage source that comes from Finland. Polar Night Energy presents its first commercial sand battery in the premises of the Vatajankoski company.
How it works.
It is a thermal energy storage system, built around a large insulated steel tank (4m wide and 7m high) filled with sand.
When this sand is heated, by means of a heat exchanger buried in the center, this device is capable of storing around 8 Mwh of energy, with a nominal power of 100 kW, with the sand heated to around 500-600ºC.
When needed, the energy is re-extracted as heat in the same way. Vatajankowski uses this stored heat, along with excess heat from its own data servers, to power the local district heating system, which uses running water to transmit heat to the area. Thus, it can be used to heat buildings, swimming pools, industrial processes or any other situation requiring heat.
The company claims it has an efficiency factor of up to 99%, is able to store heat with minimal loss for months, and has a service life of decades.
The sand is nothing special: the company says it just needs to be dry and free of combustible residue. In fact, the company considers it a very low-cost, or even zero-cost, storage medium. Everything is so simple and cheap that Polar Night Energy claims installation costs are less than 10 euros per kilowatt hour, and it works fully automated, without consumables, at minimal cost.
The company says it will also be scalable, with around 20 GWh of energy storage facilities producing hundreds of megawatts of rated power, with sand heated up to 1,000°C in some designs.
Underground bulk storage facilities can be created from disused mine shafts, if properly formed. High pressure vessels are not required and the biggest cost is usually the piping.
This sand battery, according to the company, will have its greatest impact during the freezing Finnish winter.
In fact, the solid sand storage medium is the most suitable in this case, as the design allows for multiple “zones” of energy storage in the sand. It is possible to construct a system designed for long term heat storage towards the center of the sand cylinder, but with short term cycles of repeated use closer to the top surface or outside. This would be impossible in a liquid medium such as water or molten salt, as the liquids would constantly mix and move.
More information: polarnightenergy.fi